[INVOICEUPSELLQTY1] - quantity of upsell item 1 (number can be between 1 to 20)
[INVOICEUPSELLHEADLINE1] - headline of upsell item 1 (number can be between 0 1 to 20)
[INVOICEUPSELLDESCRIPTION1] - description of upsell item 1 (number can be between 0 1 to 20)
[INVOICEEXTRAITEM1] - value of extra invoice item 1 (number can be between 0 to 20)